Roped elevator systems use a variety of configurations for the roping. In some applications, a simple 1:1 roping configuration is sufficient. In other applications, a 2:1 roping configuration is used to take advantage of the loads on the ropes being reduced by half with respect to the 1:1 roping, even though the speed of the elevator car is also reduced by half relative to 1:1 roping using the same drive machine characteristics.
The 2:1 roping configuration is achieved by placing one or two sheaves on the car to engage the ropes. If two sheaves are used, they are commonly referred to as tandem sheaves. Tandem sheaves typically comprise a pair of sheaves mounted on a sheave frame. The sheave frame is then mounted under the cross-head of the car frame. Tandem sheaves provide the advantage of accommodating large rope drops (rope center to center distance) that would be impractical with a single sheave.
One drawback to tandem sheaves is the difficulty in aligning the tandem sheaves with the drive sheave and/or the dead-end hitch point. Ideally, the ropes extending upward from the car would form little or no angle relative to vertical. Minimizing this angle improves the performance and operation of the elevator system.
Conventional systems using tandem sheaves incur a considerable amount of cost related to the engineering, manufacture and installation of the tandem sheaves. The sheave frame and cross-head must be engineered to meet the particular angle required by the installation site. Once the angle is determined and the sheave frame and cross-head are fabricated, the sheave frame must be accurately positioned and clamped under the cross-head so that the locations for fastening bolts can be identified and the holes drilled. Even with this preparation, alignment of the ropes at the installation site is difficult due to the inability to manipulate the positioning of the sheave frame and cross-head.
The above art notwithstanding, scientists and engineers under the direction of Applicant's Assignee are working to develop elevator systems that facilitate and minimize the costs associated with fabrication and installation of elevator systems.